This invention relates to a method for preserving or maintaining the softness of dried fruits, such as raisins, sultanas, prunes, dates, currants and muscats, wherein the fruit is stored in isolation or in combination with other food products, including relatively dry ready-to-eat cereal breakfast foods.
Fresh raisins and other dried fruits, even when sealed in waxed paper and foil within paperboard containers, progressively lose their softness and became hard, presumably because of moisture losses and chemical changes. The loss of softness or tenderness becomes more pronounced when the raisins are similarly packed with dry food products, such as toasted bran or corn flakes, which have a low moisture content relative to the raisins. In order to prevent rapid loss of moisture from the raisins to the cereal, it previously has been necessary to increase the moisture content of the cereal prior to packaging with raisins. The addition of moisture to the cereal, however, causes a substantial loss of crispness, which is undesirable in many such products.
The simple topical application of a humectant to a dried fruit having a relatively tough outer skin does not reliably increase the softness retention characteristics of the fruit under storage conditions, and the fruit will absorb only small amounts of the humectant through the skin. Moreover, any improvement in softness retention resulting from the initial incorporation of a high level of moisture into the fruit is quickly lost during conventional storage. Although it is possible to grind the fruit into a paste prior to treatment with humectant, the original texture and characteristics of the fruit are thereby permanently destroyed.
There are various known methods which involve the treatment of whole fruit, such as raisins, to improve storage and other qualities. For example, the Jobin U.S. Pat. No. 3,453,118 describes a process wherein raisins are soaked in a hot, weak acidic bath to improve softness retention characteristics. Additional patents which disclose the treatment of fruits with humectants or other materials are U.S. Pat. Nos. 119,441, 1,934,837, 2,278,469 and 3,006,773.
In the copending application of Charles V. Fulger and Thomas D. Morfee, Ser. No. 171,011, filed Aug. 11, 1971, now abandoned, a process is disclosed which effectively prolongs the softness retention characteristics of dried fruit by causing the fruit to absorb at least 4%, and preferably up to 6% to 10% or more, of an added humectant. According to this process, whole dried fruits, such as raisins, are dipped into a weak acid bath heated to about 120.degree.F., rinsed with water and allowed to stand briefly, dipped into glycerol and then allowed to stand for about 24 hours until the glycerol has been absorbed, and then dried to a moisture content of from about 12% to 20%. The raisins thus treated are soft, tender and flavorful and retain these characteristics for prolonged periods of storage in comparison with untreated raisins.